Present day transparent optical nodes are primarily reconfigurable optical add-drop multiplexers (ROADMs) that consist of vast numbers of parallel mini-switches or wavelength selective switches (WSSs). Such designs may be incapable of satisfying the growing demands of network access providers, and therefore large scale optical nodes are needed to handle the massive traffic loading of next generation optical networks. For example, future optical network nodes may be required to switch in the neighborhood of four hundred incoming wavelengths over four hundred outgoing wavelengths (400×400) to satisfy the bandwidth, directional, and add/drop demands of tomorrows optical metro and long-haul networks.
It may be some time before photonic integrated circuits (PICs) technology are realistically capable of providing such a large capacity at a reasonable cost. Moreover, Micro-Electromechanical Systems (MEMS) may be unsuitable from a practical standpoint, due to their being bulky, inflexible, costly, and (at times) unreliable. Accordingly, in the near-term, next-generation optical network nodes will likely be manufactured using N×N photonic switching fabrics to interconnect inputs and outputs.